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Engineering Post Frame Buildings

Engineering Post Frame Buildings

Engineering Post Frame Buildings

(OP)
I'm getting ready to do an analysis of a post frame building and I am still hunting down every resource I can find to educate myself since this is the first post frame building I have ever done. I've managed to acquire a copy of the 1999 Post-Frame Building Design Manual published by the NFBA, which appears to be the defacto standard for pole building engineering. However, online I have found other misc. papers describing a "simplified" method for designing post frame buildings.

I am wondering what others typically use as their reference and what are your thoughts on the simplified methods (Don Bender and Drew P. Mill).

I've also just noticed that the second edition of the NFBA manual has now come available.

http://www.nfba.org/index.html

Has anyone had a chance to purchase it and compare it with the 1999 edition (First Edition)?

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

I've always understood post frame to be different than a pole structure. In the pole structure, the fixing is at the ground level, and in the post frame it is at the juncture of the beam and column, leading to totally different foundations.

I suppose you could combine the two also. What do you have?

Mike McCann, PE, SE (WA)


RE: Engineering Post Frame Buildings

Sliderule's website has another pole-building reference on it if I remember correctly. I think it's by Donald Patterson.

I also use:
  • ANSI/ASAE EP 559 - Mechanically Laminated Columns
  • ANSI/ASAE EP486.1 - Shallow Post Foundation Design
  • Research papaer FPL-RP-528 by the United States Department of Agriculture
Might I also recommend if you are really stuck, Try contacting Dr. Kris Dyck at the University of Manitoba (you can get his info from their staff directory page). He is the Pole shed and hay bale house specialist.

RE: Engineering Post Frame Buildings

(OP)
6x6' posts, 4' deep. Post frame structure not a pole barn.

Is there any specialized software out there already, my ignorance may have me reinventing the wheel here.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

nope.

At least not that I've found. To be completely honest you are in for a battle with the contractor again.

These will not calc out the way he's expecting. You are going to need to use your 'What's reasonable?' hat a lot when designing these.

You can basically throw deflection requirements out the window and be prepared to take every member right to it's limit.

How tall? Dirt Floor? 4 foot embedment is unlikely to work unless the posts are spaced tightly.

RE: Engineering Post Frame Buildings

(OP)
I haven't started running any numbers yet but its not very large so I'm thinking it should calc out, we'll see...

It's only a 20x30 with posts at 10' on center, so four posts per side. A 5-1/8 x 10-1/2 Glulam beam spanning the posts on each side with mfg. trusses at 24" o/c.

14' eave height, 4/12 pitch, 24" overhangs all the way around. Originally an open design but the owner has framed in walls between the posts, so its now an enclosed structure.

Post depth is 4' with 18" Dia. holes, back filled with concrete to grade. The original plans called out #4 rebar drilled through the posts for uplift.

This is a case of the structure being built without a permit and now the building dept. has required it be engineered. The owner had assumed that he did not need a permit since the square footage was under 800 sqft.

The addition of framing and sheathing to the walls will add to the lateral strength of the structure however I think I will first neglect that contribution and see if it works with just the capacity of the poles and roof diaphragm.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

(OP)
Forgot to add dirt floor.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

My bet is it won't calc out at those spacings, but that's just my initial thought. It really will depend on height.

Make sure to use low importance when determining your loading.

Good luck with this, you're in for another tough one.

RE: Engineering Post Frame Buildings

(OP)
I've been doing some reading of different resources and I am now at a cross roads with my analysis.

I am trying to determine whether I should analyze the structure with or without diaphragm action. I am looking for pros and cons of each method and what others typically do for simple post frame structures.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

Sounds more like a pole barn to me with the 6X6 post cantilevering out of the 18" diameter X 4' deep concrete footings.

A true post-frame structure would have let-in diagonal braces framing from the columns to the beams above, columns not extending into the foundation, and hence pinned at the footing.

Mike McCann, PE, SE (WA)


RE: Engineering Post Frame Buildings

(OP)
Another question I have with the post embedment design is how to handle a post that is fully encased in concrete vs. a more traditional collar design. Would such a post be considered constrained vs. unconstrained, it seems to me that the mass of concrete encasing the post below grade will have some effect on the resultant soil forces and the bending moments and shear of the post itself.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

Depending on the wind load seen, the 14 foot eave height may kill the 6X6 columns, let alone the required embedment with only an 18" diameter footing. You will just have to run the numbers and see where you are. Hopefully you know the grade of the columns. Also check to see if they are rough cut members or not.

Mike McCann, PE, SE (WA)


RE: Engineering Post Frame Buildings

ASABE EP486 will answer all your post questions.

A post would be considered constrained at the ground surface if a concrete slab or other means was present. A post with a full collar acts just like a post without a collar, except it is much wider, therefore reducing the lateral stress on the soil. Again EP486 will answer all these questions.

A true pole structure will likely need knee and wye braces at the top of the posts, otherwise the posts act as a cantilevers. Fixed at about d/3 below the ground and pinned at the top. The Ke factor of 2 for this condition increases post sizes drastically. This may work with smaller structures. My experience is mostly 40-50' wide structures with peak heights of 20' or so. These structures typically require 8x8 or 8x10 SYP posts. These structures are designed for 60 psf gsl.

RE: Engineering Post Frame Buildings

"Originally an open design but the owner has framed in walls between the posts, so its now an enclosed structure."

From a pole frame to a shearwall structure. I used to make a pretty good living off of contractors who did that.

RE: Engineering Post Frame Buildings

Use diaphragm action and shear walls + the cantilevered columns to resist lateral loads. They show an example in the NFBA. They have some program called DAFI you can download for free. I don't like it.

In the NFBA they have tables for diaphragm and shear wall assemblies that they tested just using the metal decking as the sheathing for the walls and roof.

In my experience designing pole barns is a pain. The owner always thinks it should be cheaper.

RE: Engineering Post Frame Buildings

A professor at Cornell University did some research on the diaphragm action from light gauge sheet metal siding and roofing. I am not sure if he published the research.

RE: Engineering Post Frame Buildings

(OP)
This job is probably a bit more headache than I'm going to get paid for but once again it is an educational tool so I can accept that.

I've been doing a lot of reading the last couple of nights (last night up until 4:00AM, not sure how productive that was). DAFI is used to analyze the structure if your assuming diaphragm action, which I will probably want to do in this case since I can get some of the transverse load off of the post frames and into the gable end shearwalls.

Unlike conventional framing there are not holdowns but I'm assuming that the embedded posts at the corners of the structure can serve the same purpose.

My other burning question right now it how to deal with the tributary area for lateral loads due to wind. With conventional stud walls and roofs half the wall height and the roof height is tributary to the top of the walls and the shear load is applied at the top of the walls. For a standard post frame structure using girts the load distribution would seem to be different, wouldn't all of the wall area be considered for lateral loading to the posts in addition of course to the lateral loads coming from the roof.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

Yes your embedded posts can act as the tie-downs, but beware that it may not work as well as intended. The last time I needed belled piles to enact enough soil weight.

The NFBA manual goes through that as well.

RE: Engineering Post Frame Buildings

And for the last question,

If you are designing the posts to cantilever then your thoughts are correct, when designing the posts you need to account for the entire wall, and the roof contribution.

If you're trying to dump some of the lateral shear load into the end walls the hardest part is determining how much makes it there as opposed to how much the columns end up taking.

RE: Engineering Post Frame Buildings

Very true in that the lateral deflection of the roof diaphragm and the lateral deflection of the columns in one line transverse to the diaphragm
must equal at each column location.

Simpler to design the columns for their tributary area in the short direction and the long sidewall shearwall for half the endbay area force.

Mike McCann, PE, SE (WA)


RE: Engineering Post Frame Buildings

As Mdeek stated, these jobs are typically just very big headaches. Too much detailing for not enough money. I have stopped doing them. What about the whole,"PT wood will rot when embedded in concrete" theory?

RE: Engineering Post Frame Buildings

That's why I put 6" of gravel in the bottom of the hole. Never had a problem with rot when I did that.

Mike McCann, PE, SE (WA)


RE: Engineering Post Frame Buildings

(OP)
I was under the impression that PT wood was "good" with concrete, that is why we always use PT sill plates in conventional construction.

If you put 6" of gravel in the bottom of the hole I'm assuming that you use some type of collar (wood or concrete) otherwise the vertical bearing pressure of the posts would punch right down through that gravel. Everything I've seen so far usually calls out at least 6" of concrete in the bottom of the hole as a footing for the posts. The NFBA manual states that any friction between the posts and soil cannot be considered for vertical bearing.

With regards to the lateral load applied to the cantilevered posts: Do I mass all of the load from the roof and walls (trib. load by area for that post, transverse direction) into a point load at the eave height?

or

Do I apply a point load for the roof load at the eave height and then a rectangular distributed load from the walls to the full height of the post from the eave to grade?

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

I'd go with option 2. It gives you the best chance of actually working

RE: Engineering Post Frame Buildings

There are many different PT treatments and treatment levels. Some treatments have a long history of proven performance and others are questionable at best. Typically an oil borne treatment, such as Copper Naphthenate and Creosote, provide better long term performance. CCA is a water borne treatment that has a proven track record. Then there is the level of treatment that should be specified for the end use. The AWPA has treatment categories by end use. By specifying UC4C - Critical Structural Components, only the treatments that are suitable will be used. Most importantly, you won't find these treatments at Lowe's or Home Depot. It will have to be ordered.

RE: Engineering Post Frame Buildings

(OP)
I've decided to use the rigid diaphragm method as explained in the thesis by Drew Patrick Mill (August 2012). However with this method it is assumed that the endwalls provide the primary resistance to the load on the diaphragm (eave loading). If there is a significant opening one end of the structure then I'm assuming the posts on each side of that opening will act like segmented shearwall chords and should be embedded and sized such that they can resist the uplift and compression in this role. For example I have a 20ft end wall with a 12ft opening, 4ft of wall on each side of the door.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

(OP)
For a shearwall with a higher unit shear typically I would call out a tighter nail spacing (ie. 4" or 3" on center spacing) for walls sheathed with wood. However, I'm looking at a couple of plans by other engineers and architects where the pole frame structure is metal on wood and I don't see any specific call outs for a higher fastener count or additional girts for the endwall with the large opening and therefore higher unit shears. Am I missing something here?

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

I guessing that most "pole structures" are not designed with diaphragms.

RE: Engineering Post Frame Buildings

It's definitely what splitrings said.

Most shearwall calcs don't work as the posts are spaced too far apart for the plywood to act properly.

And the metal diaphragms don't have many published values and the ones I've seen lead me to assume they're only good for 100plf and don't screw around with the fastening (pun intended).

All of the ones I've seen designed are cantilevered columns.

RE: Engineering Post Frame Buildings

(OP)
This post frame engineering is not as simple as I thought it would. How the heck do these things get actually engineered?

I guess with this particular case I will have to assume that the endwall shear is simply taken up by the two endwall posts, cantilevered.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

A first order analysis is done as a portal frame. Two posts and a truss in between, with or without knee braces. A second order analysis can be done by moment distribution, stiffness method, etc.

RE: Engineering Post Frame Buildings

(OP)
Has anyone solved or have in their knowledge base somewhere the correct expression for the maximum positive moment in a pin/roller propped cantilever. I have the max. negative moment per Drew Mill's paper and a nifty derivation he did using slope-deflection equations. Unfortunately he did not solve for the positive moment as well.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

If you are looking at the embedded section of the pole, ASABE EP486 has the equations.

RE: Engineering Post Frame Buildings

(OP)
This is above ground. Basically this is the equivalent of a cont. beam with two unequal spans with a uniform load on one span.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

(OP)
Specifically I am looking for M1 of Figure 26 of the AWC Design Aid #6. The only difference is that the two spans are not equal. I've searched everywhere and cannot find a derived solution to this problem. I guess I will have to work it using the stiffness method, time to open up my structural analysis book...

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

As ugly as the analysis is. The pole sheds that I have actually got to calc out I had to assume fixed at the base and a spring at the top.

I then played with the spring constant until the diaphragm shear was within my allowable.

It never ends up being worth the fees but that's how I had to do it.

RE: Engineering Post Frame Buildings

(OP)
Sporadically plugging away at a spreadsheet that hopefully can completely calculate a post frame building. This is what I have so far:

http://design.medeek.com/resources/postframe/2015-...

As you can see I'm still establishing the basic loads and deflections, however in a few hours I should be able to determine if this particular structure will actually "work". The kind of cool thing with this particular calculator is that I've integrated the wind load calculator into a separate sheet so changing wind loads is a "breeze".

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

(OP)
The NFBA manual in section 8.3.5 suggests that one can take an additional twenty percent increase in allowable vertical soil pressure for each additional foot of depth, and up to a max. of three time the original value. However, I am not seeing this allowance for an increase anywhere in Section 1806 of the IBC, am I missing something?

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

In IBC 2003 it is in a footnote to table 1804.2. In IBC 2012 it is in section 1806.1. These increases are only allowed for load combinations that include wind or earthquake loads.

RE: Engineering Post Frame Buildings

(OP)
Everything seems to calc out okay until I get to the bending moments at the base of the central posts (see second to last page of pdf). The problem is I'm dealing with an "as built" so I can call out a 6x8 DF No. 1 post, I'm stuck with a 6x6 PT post that is probably a HF No. 2.

Current Spreadsheet and PDF output is here:

http://design.medeek.com/resources/postframe/

The ultimate wind speed is 155 mph (120 mph ASD) or 100 mph fastest mile. I've taken a reduction of .87 in the wind speed in order to bring this down to a Risk Category I building, which drops my ultimate wind speed to 135 mph.

Even so the combined stress on the 6x6 HF No. 2 central posts (windward side) are at 151% of the allowable.

What else more can I do to make this building work?

I've gone through the spreadsheet fairly carefully looking for any calculations errors or flaws in the methodology but it appears to be mostly sound.

Granted I haven't checked uplift yet and C&C out of plane loads to the roof and wall sheathing but that will probably be fine based on previous experience.

I've also taken a vertical pressure increase per ASAE486.1 for the footings since the jurisdiction has not adopted the more recent codes and their code books still reference this document and not the more recent ASAE486.2.


The really big problem I have if I can't get the numbers to work is that I probably will not get paid for this job. The client does not want to hear that his RV garage has to be torn down because my numbers don't work. Even if one was to retrofit the central posts by sistering 2x6's onto the appropriate face, this would still not really help with the max. moment occurring right at the ground line. If I can't get it to work the customer will probably hire another engineer who can make it work.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

Are you sure the PT post is HF? You sure it isn't SYP?

RE: Engineering Post Frame Buildings

50% isn't as bad as I've seen some so you've got that going for you.

Have you really trimmed down your roof dead loads (I know it hurts the uplift calcs but those are easier to deal with usually). It likely won't get you to passing but it may trim a few percent off of the code check.

I would get confirmation on the post species and grade if possible that way you have an accurate capacity.

If you got this down to 120% or less I would be impressed. The existing ones don't calc out as we all have been saying the whole time.

You could knee brace the columns and it might get you enough.

RE: Engineering Post Frame Buildings

(OP)
A HF No. 1 will work, :)

Now the final piece of the puzzle...

I'm looking at the uplift resistance of a 18" dia. by 4' deep post hole backfilled with concrete. At 150 pcf the concrete donut basically weighs 934 lbs. My basic uplift from the wind combined with 0.6 of the dead loads is only 703 lbs so that works.

However, to get an additional margin I would like to include a value for the skin friction between the soil and the concrete cylinder. I'm not seeing an example of that calculation in any of the resources and texts I'm looking at.

Then of course there is the problem of the corner posts which are acting as the shearwall chords and resisting the lateral loads. They have a certain uplift which is countered by the roof and wall dead load to some extent 7.) 0.6D + 0.6W and the uplift capacity of the backfill.

In my opinion these types of structures are an engineer's nightmare. There is way too much going on with these posts both vertically and laterally. A conventionally framed structure distributes the loads far better and is easier to analyze. I've spent the entire week trying to spreadsheet this thing and I know my analysis is still far from adequate or complete.


A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

(OP)
So this is interesting:

If I assume a 6" deep circular collar at the base of the post (4' embedment) I then am able to take the cone of soil per 8.9.4 of the NFBA manual which is 3,893 lbs.

However, if I assume concrete backfill to the surface then all I have is the weight of the concrete in the hole minus the post area which gives 934 lbs.

Does this not seem somehow counter intuitive? Wouldn't the concrete lift some of the soil with it in a full on uplift situation?

The question is how to quantify this.

8.9.3 of the NFBA manual states that concrete backfill gives an uplift resistance of the mass of the concrete plus skin friction but then gives no further guidance.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

(OP)
The customer wants to leave the front of the carport open so I am looking at doing a sheathed kneewall brace, if such a thing exists. The idea is to create something similar to a portal frame at the front of the structure. I'm not sure how to apply any numbers to this though yet, still rolling it around with a couple of other ideas.

I'm thinking it will put a concentrated load on the corner post 4' feet down from the eave as well as a similar load on the 20' fink truss above. There is a double 2x6 top plate below the fink truss but this is not the same as a deep beam that can accommodate the bending loads.

Has anyone run into something like this before? Any suggestions?

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

The national frame building association used to put on webinars about every other month going over industry standard designs. Contact them to see if you could maybe get a copy of the slides or maybe they have one recorded. I found them to be helpful. I may have a pdf of the slides if I can find it.

EIT
www.HowToEngineer.com

RE: Engineering Post Frame Buildings

My geotechnical expertise is pretty weak but I am guessing the skin friction between the full concrete collar and soil is insufficient to engage the available shear strength of the surrounding soil. I just looked at the new ASABE EP486-12 and it states a "device that enlarges the base" can use the uplift resistance provided by soil. The commentary include with the draft of this reference did directly state that without the enlarged base only skin friction should be considered.

RE: Engineering Post Frame Buildings

(OP)
I just found Breyer's example problem 12.8 for a knee wall brace, I will use this for a guide.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

Just so you know... post-framed buildings are framed after the building is erected.

It's Friday...

Mike McCann, PE, SE (WA)


RE: Engineering Post Frame Buildings

Quote (msquared48)

It's Friday...

...and a 'good' Friday for some...

RE: Engineering Post Frame Buildings

(OP)
I wish it was a Friday for me right now. This post frame building has been nothing but grief.

The full analysis of the post frame is here for those interested:

http://design.medeek.com/resources/postframe/


Assuming that the structure transfers the bulk of its lateral loads to the end walls (shearwalls A and B) and the post frames on grid lines 2 and 3 do not offer any significant resistance I get a shear load of Vw = 1630 lbs, which doesn't sound like a lot.

So I then run the following manual calcs to determine if a 4' diagonal knee brace will work on the one end wall:





The axial force in my knee brace is a whopping 4,034 lbs.

I then check to see what effect that might have on one of my 6x6 HF No. 1 corner posts:



As you can see it does not work, not even close.

The loads on the horizontal header would also require some beefing up of the gable end truss bottom chord but that can easily be arranged.

With respect to the knee brace and the corner post I don't think sheathing the knee brace will do much to decrease the bending moment in the corner post but I could be wrong. Any suggestions?

I thought of a few different solutions:

1.) Tell the client knee bracing won't work and make him install two additional end wall posts to create a 12' wide door as I originally envisioned he might do.
2.) Sister another 6x6 or even 4x6 post to the existing corner post to get more bending strength, attached the to posts with some counter sunk lag bolts and sheathing.
3.) Somehow analyze the knee brace differently so that my axial force in this member is decreased?
4.) Re-analyze the entire post frame building treating the roof diaphgram as rigid, essentially a three wall structure. The problem with this is that it doesn't really agree well with other accepted methods of assigning shear loads to post frame buildings (ie. NFBA manual etc...)

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

(OP)
Here is the popsicle stick and cardboard analog. It helps to have a physical model to get a feel for all of the forces and deflections of the members...

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

(OP)
Number 3 and 4 were kind of the answer. My original analysis assumed a pin joint at the ground, this throws all of the lateral resistance onto the knee brace. In reality we have the two knee braces and the embededded posts resisting the lateral loads. When I tried to run the statics equations by hand using the pin/roller @ .7d modeling method things got too hairy for my liking so I put it into Risa3D:



Actually, before I ran with RISA, I first checked to see what would happen if just the embedded posts tried to resist the load without any knee braces and assuming 815 lbs at 14 ft off the ground I get a 11,410 ft-lbs ground line moment. That certainly wasn't going to work.

Anyhow, even with the reduction in moments and assuming a DF No. 1 post the numbers are still too high. Bending wise it comes in at about 98% but then if you add in the axial and calculate the combined stress index its about 170%.

However, putting it into RISA was a good idea since I got a deflection at the eave that manually I could never have reasonably calculated. The deflection is about 2.2", which is extremely large compared to the deflection of the roof diaphragm (7/16" OSB sheathing on 24" o/c trusses). So given that I can assume a rigid diaphragm and basically throw most of my calculations out the window...

The question is now do I really need any sort of knee bracing at all. The three other walls are fully sheathed with 15/32 plywood, plenty of shearwall and stiffness and no windows or doors.

I kind of wish I knew RISA a little better, I would probably put the whole structure into it and let it figure out what component (post, shearwall, knee braces etc...) is actually taking the lateral loads.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

(OP)
I basically already was considering the diaphragm as perfectly rigid by utilizing the simplified method from Drew Mills paper. The problem with my analysis was that I was distributing the reactions from the diaphragm to the endwalls equally. Obviously this is not the case. A more realistic approach would be to look at the center of the rigidity with respect to the center of the load and proportion the shear loads to the shear walls per the example in Ch. 16 of Breyer's text. This was my final approach, the tricky part was to determine a realistic but yet conservative value for the stiffness of the endwall braced only with knee braces. Based on the deflections generated in RISA (2.2" for a lateral load of 1630 lbs, my shearwall stiffness would then be approx. 730 lbs/in or .7 kips/in. This extremely low value when input into the calculator yielded such a low lateral load that it seemed prudent to use a higher stiffness to give the knee braced wall a greater load.

I think I finally have a handle on this one but after so much trouble in making it "work" I'm left thinking that maybe there is something else that I have not accounted for that will pop up and invalidate the entire updated set of calculations.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

Medeek -> first I appreciate your efforts in digging through all post-framed material and posting your thoughts here. Second,

Quote:

The three other walls are fully sheathed with 15/32 plywood, plenty of shearwall and stiffness and no windows or doors
So you have sheathed walls? Why not just use these for your LFRS?

EIT
www.HowToEngineer.com

RE: Engineering Post Frame Buildings

Rfreund,

There was a fair amount of discussion a while back as to whether 3-sided shear wall structures were acceptable. I'll continue to watch this thread with interest.

RE: Engineering Post Frame Buildings

You show a pinned condition at nodes N9 and N10 of your RISA model. If this represents your ground surface, it is likely much too stiff for soil backfill. If you had a slab on grade that was constraining your post, a pinned condition may be more realistic. If you have soil backfill, I would recommend lateral springs or a fixed condition some distance below the ground surface. ASABE used to suggest a distance below the ground surface of d/3 but now they are recommending a distance equal to width of the pole. The later seems short to me.

RE: Engineering Post Frame Buildings

(OP)
The decision to go with a pinned connection was made after a phone conversation with the client. Currently the garage is a dirt floor but he has decided to pour a stemwall around the perimeter with a slab that connects to the 18" DIA x 48" concrete backfilled holes.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Engineering Post Frame Buildings

Sorry I was confusing "3-walls" meaning 3-sided box with 3 lines of shear walls. Welp, carry on...

EIT
www.HowToEngineer.com

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